1. Technical Field
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal device capable of improving transmittance characteristics.
2. Related Art
In the related art, as liquid crystal display devices capable of providing a high contrast ratio and a wide viewing angle, a liquid crystal display device is known in which the alignment of liquid crystal molecules is controlled by using an electric field generated in a direction approximately parallel to two transparent substrates having liquid crystals sandwiched therebetween. That is, a liquid crystal display device is known that is operated in a fringe-field switching (FFS) mode or an in-plain switching (IPS) mode. In such a liquid crystal display device, on one of the two transparent substrates, a pixel electrode to which a display signal is supplied and a common electrode to which a common potential is supplied are arranged.
In an liquid crystal display device that is operated in an FFS mode, a plurality of linear portions and a plurality of slits are arranged in the pixel electrode so as to alternate in parallel to each other, and the pixel electrode and the common electrode are disposed opposite each other with an insulating film disposed therebetween. The liquid crystal molecules are initially aligned in accordance with a rubbing direction of an alignment film. When the display signal is applied to the pixel electrode, an electric field that extends from the linear portions of the pixel electrode to the common electrode that extends on a lower layer of the slits is generated in a direction approximately parallel to the transparent substrate, and the alignment direction of the liquid crystal molecules is controlled in accordance with the electric field. An optical control is carried out via the liquid crystal molecules so that images are displayed as white or black.
For example, in Page 1 and FIG. 3 of JP-A-2002-182230, an FFS mode liquid crystal display device is disclosed, in which first and second transparent insulating substrates ate arranged opposite to each other at a predetermined distance, with a liquid crystal layer including a plurality of liquid crystal molecules interposed between them. A plurality of gate bus lines and a plurality of data bus lines are formed on the first transparent insulating substrate so as to be arranged in a matrix form to define a unit pixel. A thin film transistor is formed at intersections of the gate bus lines and the data bus lines. A counter electrode made of a transparent conductor is disposed in each unit pixel. A pixel electrode made of a transparent conductor is arranged in each unit pixel to generate a fringe field with the counter electrode so as to be isolated from the counter electrode, including a plurality of upper slits and a plurality of lower slits that are symmetrical each other with respect to longer sides of the pixel with a predetermined tilt angle.
In the FFS mode liquid crystal display device disclosed in JP-A-2002-182230, a rectangular pixel electrode is disposed at a region surrounded by the gate bus line and the data bus line. A plurality of slits that is inclined with respect to the shorter sides parallel to the gate bus line is formed in parallel to each other in the pixel electrode. The upper slits and the lower slits are formed such that the tilt angles thereof are symmetrical each other at a central position in the longitudinal direction of the pixel electrode. Therefore, it is possible to improve the transmittance by the slit configuration. However, since the pixel electrode has a rectangular shape and has slits that are inclined with respect to the shorter sides of the rectangle, an electrode portion having a rectangular equilateral triangular shape remains formed between the slits close to the opposite outer edges on the lower sides and a fringe of the pixel electrode. Therefore, the transmittance is lowered in the electrode portion.